The present invention concerns a system, and corresponding method, for scanning a real object. The object of the scanning may be an entire article, or a portion thereof, or the surface or portion of the surface of an article. The system and method of the invention is capable of the acquisition of geometry and material surface reflectance properties of the object of the scanning. Examples of such material surface reflectance properties include the surface colour and specularity, which may also be referred to as reflectance properties.
Systems are known for 3D geometric acquisition of the shape of an object, for example as disclosed in WO 2005/040850. However, geometric information alone is not always sufficient for particular scanning applications, such as full colour model acquisition for example for video games and animated films (e.g. scanning and reconstructing a figure for subsequent animation), interactive visualization (e.g. for medical uses or for academic use such as scanning antiquities for subsequent study), and quality control (e.g. inspecting the surface finish of an object for desired gloss or satin finish, inspecting completeness of paintwork on a painted object).
Other systems are known for acquiring information on an object via “photometric stereo” (PS), i.e. obtaining spatial information on the properties of the interaction of the surface of an object with light. FIG. 1 shows an example of a traditional hardware setup for object acquisition via photometric stereo. A single camera 100 is positioned to capture images of an object 101 illuminated individually and sequentially by a number of light sources 102, 103, 104, the geometrical positions of the light sources with respect to the object having been obtained via prior calibration. In FIG. 1 three light sources are shown, which represents a typical minimum setup. However, there are problems and limitations with such a system: for example, depending on the material reflectance model used, the determination of the PS information for the object can be intractable or require an extremely large amount of processing power or time. The range of applicable materials may be very limited, for example objects which exhibit specular reflection cannot be correctly acquired. The use of additional light sources and more advanced reflection models can assist, but this increases the hardware requirements and the difficulty of calibration. Furthermore, a PS system as described above is inconvenient to operate and to set up, in particular multiple geometrically and radiometrically calibrated light sources are required. It does not lend itself to enabling convenient, moveable (such as hand-held) scanners to be achieved. PS data in which the geometry is recovered by integration also suffers from the problem of being “non-metric” in the sense that it does not provide absolute height, width and breadth information, and can be subject to low-frequency drift due to the integration, implying a possible curvature in space.
A further problem is to register and combine, i.e. reconcile, geometric data and photometric data for an object acquired with different techniques.
The present invention aims to alleviate, at least partially, one or more of the above problems.
Accordingly, the present invention provides a scanner system for scanning an object, the system comprising:
a scanner device; a target; and a processor,
wherein the scanner device comprises: an emitter for projecting patterned light on the object; and a sensor for capturing images of the object,
wherein the target has predetermined features visible to the sensor simultaneously with the object for enabling the processor to determine the location of the sensor with respect to the object,
wherein the processor is arranged, in use, to generate geometric data, comprising a three-dimensional model of the object, on the basis of images of the object with the patterned light projected thereon by the emitter,
wherein the scanner device further comprises a light source for directionally illuminating the object, and the sensor is arranged to capture images of the object illuminated by the light source,
wherein the processor is arranged, in use, to generate sets of photometric data for the object when illuminated from different directions by the light source, and
wherein the processor is arranged, in use, to combine the geometric data and photometric data to output a model comprising geometric information on the object together with photometric information spatially registered with the geometric information.
The present invention also provides a method for scanning an object comprising steps of:
providing a target that has predetermined features, and capturing images of the object and target features simultaneously using a sensor;
determining the location of the sensor with respect to the object on the basis of the captured images;
projecting patterned light on the object;
generating geometric data, comprising a three-dimensional model of the object, on the basis of images of the object with the patterned light projected thereon;
directionally illuminating the object using a light source;
generating sets of photometric data for the object when illuminated from different directions by the light source; and
combining the geometric data and photometric data to output a model comprising geometric information on the object together with photometric information spatially registered with the geometric information.
A system embodying the invention is able to offer advantages including improved accuracy, reduced cost and increased usability over conventional technologies, and may be produced in a portable hand-held package. As well as the standard applications for 3D geometric acquisition (such as e.g. reverse engineering, quality control), the system's ability to capture material surface reflectance properties such as inhomogenous colour and specularity make it applicable for a wide range of other fields, such as full colour model acquisition, interactive visualization, and material analysis for example quality inspection of paint work or surface finish.
A system or method embodying the invention advantageously only requires a single sensor (e.g. camera) for capturing images of the object. Furthermore, a system embodying the invention advantageously only requires a single light source, which may be a composite light source, but the light source can be compact with a maximum dimension of say 150 mm or smaller. Also, additional backlighting sources are not required. All of these features enable the scanner device of the invention to be made portable, and preferably hand-held. Of course, multiple light sources may optionally be used if the application requires it, but the scanner device itself can still be a single, portable, preferably hand-held unit,